1. Field of the Invention
The present invention relates to brightness control in a visual information display system, and more particularly relates to adjusting the brightness level to compensate for changes in ambient lighting.
2. Description of the Related Art
Backlight is needed to illuminate a screen to make a visible display in liquid crystal display (LCD) applications. The ability to read the display is hampered under conditions of high ambient room lighting. Ambient lighting reflects off the surface of the LCD and adds a bias to the light produced by the LCD, which reduces the display contrast to give the LCD a washed-out appearance. The condition can be improved by increasing the brightness of the backlight for the LCD, thereby making the light provided by the LCD brighter in comparison to the reflected light off the LCD surface. Thus, the backlight should be adjusted to be brighter for high ambient lighting conditions and less bright for low ambient lighting conditions to maintain consistent perceived brightness.
In battery operated systems, such as notebook computers, it is advantageous to reduce power consumption and extend the run time on a battery between charges. One method of reducing power consumption, and therefore extending battery run time, is to reduce the backlight brightness of a LCD under low ambient lighting conditions. The backlight can operate at a lower brightness level for low ambient lighting conditions because light reflections caused by the ambient light are lower and produce less of a washed-out effect. It is also advantageous to turn down the backlight under low ambient lighting conditions to extend the life of light sources in the backlight system. Typically, the light sources have a longer lifetime between failures if they run at lower brightness levels.
In some LCD applications, an ambient light sensor is used in a closed-loop configuration to adjust the backlight level in response to the ambient light level. These systems usually do not take into account user preferences. These systems are crude in implementation and do not adapt well to user preferences which may vary under various levels of eye fatigue.